Abstract : NEXUS is a research project which is concerned with input processing of natural language for information retrieval. The computer program used to do this task consists of linguistic rules that operate on the suffix portions of printed words, and the order of these words as they appear in a sentence. NEXUS accepts lists of index terms that have resulted from the application of an auto-indexer program to titles and abstracts. These term lists are processed by NEXUS in order to form combinations of terms which are stored as subject headings. Such subject headings or precoordinations aid the searcher in finding information when they are used in a bibliographic printout. As opposed to coordinate-indexed printouts, consisting of lists of individual terms and the accession numbers of the source documents, those printouts of NEXUS processed terms contain word combinations that have been precoordinated, saving time and increasing accuracy for the searcher. Comparison tests have been run using the full NEXUS program, a partial application of the program using sequence rules (SEQS) and human analysis of the same data. Although falling short of human analysis in some respects (except for consistency), the NEXUS approach is more effective than SEQS in producing effective combinations. The chief value of this effort has been to further study those aspects of language that are amenable to computerized analysis for the purpose of improving input and output functions in information retrieval. (Author)